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I'm reinsulating an exterior wall where the interior drywall and original unfaced batts were damaged. The inside surface of the exterior wall appears to be a foil-covered foam board. Should I insulate between the 2x6 studs with unfaced batts again, or would it be better to use faced? I'm a little worried about the insulation not being able to "breathe" between the drywall/kraftpaper on one side and the foil-covered foam board on the other. Thank you!
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Re: Question on insulation
Fri, October 23, 2009 - 5:32 AMAs much as the manufacturers make claims as to the value of their facing as a thermal or moisture barrier, for the most part the fold out kraft paper serves as a means to staple up the batts securely in vertical or overhead applications.
As for the insulation being able to "breathe", I take it you are concerned about condensation not air breathing or movement: Blown fiberglass insulation essentially utilizes encapsulated air spaces mainly as a communicative barrier for a thermal medium. In plain terms it blocks thermal and radiant energy forcing the transfer of energy( that can't be ffectively reflected back) to move from one minute pocket or cell to another then another etc. thereby damping or slowing the communication of energy.
In an efficient wall construction, there ideally shouldn't be substantial air movement. There should be an effective moisture barrier at the exterior envelope AND an effective air barrier at the interior envelope. So seal around all the electrical boxes, where the elec. romex enters elec boxes, ANY penetration of the drywall envelope, any air gaps, holes, notches or holes in the framing which communicate with any other distinct framing space such as the ceiling, floor, or passages framed for HVAC etc.
So go ahead and use unfaced batts. Recently, batts termed "encapsulated are being used more and more and can help if you can't control the possibility of moisture or condensation. Plus sleeved fiberglass is a lot nicer to install. -
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Re: Question on insulation
Fri, October 23, 2009 - 7:30 AMImportant point : vapor barrier.
Many installers will hang sheets of mylar/visquine (clear plastic) onto the framing before insulation installation. The vapor barrier, as the name implies, serves to prevent water condensing inside the insulation layer, rather having the condensation occur facing outwards where it drains off without compromising insulating effect.
= More bang for your buck when it comes to keeping inside space cozy & toasty. -
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Re: Question on insulation
Fri, October 23, 2009 - 9:52 AMThe application of a membrane vapor barrier varies widely from installer to installer, with region, with predominant regional climate and weather, and with the particular design and type of wall construction. It comes as no great surprise in design and the trades that even if all the previously mentioned variations didn't come into play, for every 3 builders or architectural detailers there are 4 opinions on the subject.
Ahhh, to revisit the great "Tyvek" vs. building paper debates of my youth.....
or the earthshaking "hyper sealed" vs. breathable/drain allowing envelope fracas of '89....
But depending on the seasonal dewpoint variations within Carol's particular wall section and type, it is possible that there is good likelihood that a polyethylene or 'visqueen' membrane on the interior will instigate the collection and puddling of condensation and possibly prevent the dispersal or absorption of the possible destructive moisture. Who knows....
I ain't gonna fly all the way to Carol's place to revisit my energy engineering work and do the Thermal/Moisture/Energy budget profile for her.
I'd say don't bother with the lastic: I've riped apart plenty of houses with rot/insulation failure/ energy issues that had plastic installed - either worsening the issues or simply being impossible to look to for any value due to it not being anything close to an engineered self sealing product like Tyvek that still has its ownadditional spec'd tape and sealants make a good seal. -
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Oh my. I should been a highpriestie professor of Architectural Detail... Would it pay a good wage I wonder?... Would the chicks dig it?...
Fri, October 23, 2009 - 9:55 AMHeh...
And that is all the insulation discourse I think I can possibly muster....
...for quite some time to come as well -
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Re: Oh my. I should been a highpriestie professor of Architectural Detail... Would it pay a good wage I wonder?... Would the chicks dig it?...
Fri, October 23, 2009 - 2:10 PMYou're probably right about that. My info is from hearsay, never having installed the poly vapor layer. There was alot of talk on it back in the 1980s energy credits for improvements boom.
Yes it always made me wonder about how one could be sure that the condensation stayed out rather than soaking the insulation from inside due to household generated humidity (breath, cooking, bathing vapors). So I'll have to withdraw that piece of building lore from this thread.
Likely the best shot is to have the insulation breathe and permit passage of humidity through permeability. -
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For some households in certain climates, it makes perfect sense, however.
Sun, October 25, 2009 - 9:31 AMDrier places in the country where humidity & mold are not big issues.
Houses where there is good ventilation.
Here it should not be an issue.
I take it back.
For some, hanging a vapor barrier makes perfect sense... and pays energy dividends as well.
Look into it.
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